Spectroscopic
evidence for the presence of helium in the sun was first obtained during a
solar eclipse in 1868. A bright yellow emission line was observed and was
later shown to correspond to no known element; the new element was named by
J. N. Lockyer and E. Frankland from helios [the Greek word for sun]. Helium
was isolated (1895) from a sample of the uranium mineral cleveite by Sir William
Ramsay.

areas
of use

Helium's
noncombustibility and buoyancy (second only to hydrogen) make it the most
suitable gas for balloons and other lighter-than-air craft. A mixture of helium
and oxygen is often supplied as a breathing mixture for deep-sea divers and
caisson workers and is used in decompression chambers; because helium is less
soluble in human blood than nitrogen, its use reduces the risk of caisson
disease, or the bends. Helium can also be used wherever an unreactive atmosphere
is needed, e.g., in electric arc welding, in growing crystals of silicon and
germanium for semiconductors, and in refining titanium and zirconium metals.
It is also used to pressurize the fuel tanks of liquid-fueled rockets. Liquid
helium is essential for many low temperature applications.

Within
the university the main use of liquid helium is the cooling of "cryostats",
a sophisticated measuring instrument based on a superconductive magnet, used
within areas of research like solid state physics, atomic physics och biochemistry.

helium
is a natural resource and is extracted from natural gas

Helium is rare and costly. Wells in Texas (where the Federal Helium Reserve
was established in 1925 near Amarillo), Oklahoma, and Kansas are the principal
world source, but minor wells are also found in Algeria, Poland and Russia.
Crude helium is separated by liquefying the other gases present in the natural
gas; it is then either further purified or stored for later purification and
use. Some helium is extracted directly from the atmosphere; the gas is also
found in certain uranium minerals and in some mineral waters, but not in economic
quantities. It has been estimated that helium makes up only about 0.000001%
of the combined weight of the earth's atmosphere and crust; it is most concentrated
in the exosphere, which is the outermost region of the atmosphere, 600-1500
mi (960-2400 km) above the earth's surface. Helium is abundant in outer space;
it makes up about 23% of the mass of the visible universe. It is the end product
of energy-releasing fusion processes in stars (see interstellar matter).

liquid
helium from source to customer

The
typical path starts in Wyoming, USA where helium gas is extracted from natural
gas well and liquefied at a local plant. This is filled into isolated containers
and then transported over land to a harbour in New York. After a two weeks
journey with a ship the container is loaded on trucks for road transport to
a variety of destinations in Europa. Kryolab have two 500 liters LHe-dewars
which is regularly transported to Lidingö (near Stockholm) where AGA
fills it from one of these containers. At arrival in Lund, the LHe is then
transferred into smaller dewars - usually 30 to 100 liters - according to
the customers needs.

low-temperature
physics

Low-temperature
physics, science concerned with the production and maintenance of temperatures
much below normal, down to almost absolute zero, and with various phenomena
that occur only at such temperatures. The temperature scale used in low-temperature
physics is the Kelvin temperature scale, or absolute temperature scale, which
is based on the behavior of an idealized gas. Low-temperature physics is also
known as cryogenics, from the Greek meaning "producing cold". Low temperatures
are achieved by removing energy from a substance. This may be done in various
ways. The simplest way to cool a substance is to bring it into contact with
another substance that is already at a low temperature. Ordinary ice, dry
ice (solid carbon dioxide), and liquid air may be used successively to cool
a substance down to about 80 K (about minus 190 C). The heat is removed by
conduction, passing from the substance to be cooled to the colder substance
in contact with it. If the colder substance is a liquefied gas, considerable
heat can be removed as the liquid reverts to its gaseous state, since it will
absorb its latent heat of vaporization during the transition. Various liquefied
gases can be used in this manner to cool a substance to as low as 4.2 K, the
boiling point of liquid helium. If the vapor over the liquid helium is continually
pumped away, even lower temperatures, down to less than 1 K, can be achieved
because more helium must evaporate to maintain the proper vapor pressure of
the liquid helium. Most processes used to reduce the temperature below this
level involve the heat energy that is associated with magnetization. Successive
magnetization and demagnetization under the proper combination of conditions
can lower the temperature to only about a millionth of a degree above absolute
zero. Reaching such low temperatures becomes increasingly difficult, as each
temperature drop requires finding some kind of energy within the substance
and then devising a means of removing this energy. Moreover, according to
the third law of thermodynamics, it is theoretically impossible to reduce
a substance to absolute zero by any finite number of processes. Superconductivity
and superfluidity have traditionally been thought of as phenomena that occur
only at temperatures near absolute zero, but by the late 1980s several materials
that exhibit superconductivity at temperatures exceeding 100 K had been found.
Superconductivity is the vanishing of all electrical resistance in certain
substances when they reach a transition temperature that varies from one substance
to another; this effect can be used to produce powerful superconducting magnets.
Superfluidity occurs in liquid helium and leads to the tendency of liquid
helium to flow over the sides of any container it is placed in without being
stopped by friction or gravity.

liquefaction

Liquefaction,
change of a substance from the solid or the gaseous state to the liquid state.
Since the different states of matter correspond to different amounts of energy
of the molecules making up the substance, energy in the form of heat must
either be supplied to a substance or be removed from the substance in order
to change its state. Thus, changing a solid to a liquid or a liquid to a gas
requires the addition of heat, while changing a gas to a liquid or a liquid
to a solid requires the removal of heat. In the liquefaction of gases, extreme
cooling is not necessary, for if a gas is held in a confined space and is
subjected to high pressure, heat is given off as it undergoes compression
and it turns eventually to a liquid. Some cooling is, however, necessary;
it was discovered by Thomas Andrews in 1869 that each gas has a definite temperature,
called its critical temperature, above which it cannot be liquefied, no matter
what pressure is exerted upon it. A gas must, therefore, be cooled below its
critical temperature before it can be liquefied. When a gas is compressed
its molecules are forced closer together and, their vibratory motion being
reduced, heat is given off. As compression proceeds, the speed of the molecules
and the distances between them continue to decrease, until eventually the
substance undergoes change of state and becomes liquid. Although before the
19th cent. a number of scientists had experimented in liquefying gases, Davy
and Faraday are usually credited with being the first to achieve success.
The production of liquefied gases in large quantities (and consequently their
use in refrigeration) was made possible by the work of Z. F. Wroblewski and
K. S. Olszewski, two Polish scientists. The work of Sir James Dewar is also
important, especially in the liquefaction of air and its change to a solid.
Heike Kamerlingh Onnes first liquefied helium. The critical temperature of
helium is minus 267.9 C, only a few degrees above absolute zero (minus 273.15
C). The processes for the liquefaction of gases as developed by Linde and
others form the basis for those used in modern refrigeration.

Kelvin
temperature scale

Kelvin
temperature scale, a temperature scale having an absolute zero below which
temperatures do not exist. Absolute zero, or 0íK, is the temperature at which
molecular energy is a minimum, and it corresponds to a temperature of minus
273.15 C on the Celsius temperature scale. The Kelvin degree is the same size
as the Celsius degree; hence the two reference temperatures, the freezing
point of water (0 C), and the boiling point of water (100 C), correspond to
273.15 K and 373.15 K, respectively. When writing temperatures in the Kelvin
scale, it is the convention to omit the degree symbol and merely use the letter
K. The temperature scale is named after the British mathematician and physicist
William Thomson Kelvin, who proposed it in 1848.

Bose-Einstein
condensate

Bose-Einstein
condensate, a gas of atoms that has been so chilled that their motion is virtually
halted and as a consequence they lose their separate identities and merge
into a single entity. The condensate was predicted by Albert Einstein in 1924
based on the system of quantum statistics formulated by the Indian mathematician
Satyendra Nath Bose. Quantum theory asserts that atoms and other elementary
particles can be thought of as waves. Einstein proposed that as atoms approach
absolute zero (minus 273.15 C), the waves expand in inverse proportion to
their momentum until they fall into the same quantum state and finally overlap,
essentially behaving like a single atom. The phenomenon could not be observed,
however, until techniques were developed to reduce temperatures to within
20 billionths of a degree above absolute zero. In 1995 Eric A. Cornell and
Carl E. Wieman led a team that isolated a rubidium Bose-Einstein condensate
under laboratory conditions. It is believed that this state of matter could
never have existed naturally anywhere in the universe, since the low temperatures
required for its existence cannot be found, even in outer space. The condensate
may be useful in the study of superconductivity (the ability of some materials
to conduct electrical current without any resistance) and superfluidity (the
ability of some materials to flow without resistance) and in refining measurements
of time and distance.